1. Technical Field
The present invention relates in general to an improved data access and storage system, and in particular to an improved system and method of damping vibration on a coil support in a high performance disk drive with a rotary actuator.
2. Description of the Prior Art
Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).
A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
Modern HDD throughput and storage capacity have been substantially increased by improvement in actuator design which has resulted in increased precision and speed in head placement. The more precisely the actuator can place the read/write head, the greater the drive track density. The term “servo bandwidth” denotes the cross-over frequency of an open loop transfer function applied to head positioning systems. As the track densities of HDDs increase, a high servo bandwidth is typically required to improve the Track Measurement Registration (TMR) performance. Mechanical resonance of the coil and carriage is one of the dominant factors that limit the servo bandwidth of a voice coil driven HDD. In addition, the demand for increased speed and storage capacity has resulted in ever faster and more compact hard disk drive (HDD) assemblies. Modern, high performance disk drives typically have several stacked disks that spin on a shaft at speeds exceeding 10,000 rpm. The track densities on these disks are often more than 12,000 tracks per inch (TPI). As the track density of HDDs increases, a high servo bandwidth becomes even more important to improve the efficiency of read/write operations as measured by TMR as well as other performance indicators.
In the prior art, a number of devices for and methods of improving dynamics settling performance have been proposed. For example, U.S. Pat. No. 5,930,071 to Back, U.S. Pat. No. 5,914,837 to Edwards, and U.S. Pat. No. 5,666,242 to Edwards, all address conventional methods of damping vibration at the pivot assembly. Other U.S. Patents, such as U.S. Pat. No. 6,310,749 to Beatty, and U.S. Pat. No. 5,936,808 to Huang, focus on vibration damping in the actuator arm. Still other U.S. Patents are directed to actuator damping. Examples of this latter type include U.S. Pat. No. 5,790,348 to Alfred, which utilizes plastic overmolding on the coil. This method is not appropriate for high performance disk drives since they require high stiffness in the coil supports to allow high TPI. U.S. Pat. No. 4,602,175 to Castagna, uses a damping layer in the coil bobbin, which also reduces the stiffness of the coil itself, thereby losing damping effectiveness due to the high temperature of the damping layer. Again, this solution will not work in high performance drives since they require high coil stiffness to allow high TPI. See also U.S. Pat. No. 5,764,441 to Aruga. Thus, it would be desirable to provide an improved method and system for minimizing the contribution of dynamic mechanical deformation of a HDD suspension and head apparatus to the off-track position error of read/write heads in a digital system. If implemented, such a system would serve to increase the access time, performance, and effective track density of a HDD assembly.